This invention relates to a distributor-type fuel injection pump for internal combustion engines, and more particularly to a fuel injection pump of this kind which has a function of varying the injection rate in response to operating conditions of the engine.
An injection rate control system for a distributor-type fuel injection pump has been proposed, which is adapted to vary the injection rate in response to operating conditions of the engine, by Japanese Provisional Patent Publication (Kokai) No. 57-65857. This injection rate control system comprises two pump working chambers defined, respectively, a portion with a larger diameter and a portion with a smaller diameter of a plunger, which makes a concurrent reciprocating and rotative motion for delivery and distribution of fuel into cylinders of the engine, and selector means for selectively causing one or both of the two pump working chambers to take part in fuel injection, to thereby vary the injection rate.
According to this injection rate control system, when the engine is operating in a high speed/high load region, the two pump working chambers are both made to operate for fuel injection, while when the engine is operating in a low speed/low load region, only one of the chambers is made to operate for fuel injection. In the latter case, as a changeover is made from the concurrent operation of the two pump working chambers to the single operation of only one of the chambers, the injection quantity is suddenly reduced by a considerable amount to cause a sudden large drop in the engine rotational speed, impairing the driveability of the engine.